The family environments in which children are born and raised have a profound influence on their behavior, education, and health (Amato 2001; Cherlin 1999; McLanahan & Sandefur 2009). With the overlapping demographic and social trends of later age at marriage, greater acceptability of divorce and non-marital childbearing, and more cohabitation, the landscape of American families is diverse and dynamic. According to the recent Census, 29% of American children live with only one biological parent, and 3.5% reside with neither biological parent (Vespa et al. 2013). Such cross-sectional estimates, however, belie the true complexity and dynamism of family structures. Not only do children increasingly live in diverse family forms, but the childhood experience of family structure is dynamic, with children likely to live in a variety of families by the time they reach adulthood (Cavanagh & Huston 2006; Graefe & Lichter 1999; Heuveline et al. 2003). Using nationally representative integrated demographic, social, contextual and biological data on children in the United States, the proposed study will trace the biological pathways through which childhood family instability influences adult health. The Investigator hypothesizes that family instability creates intense and chronic stress that will be evident in measures of adult stress reactivity and that have negative long-term health consequences. The project will evaluate the importance of instability during sensitive developmental stages of early childhood and adolescence, and investigate gender, race and ethnic differences in stress response processes. This project contributes to the field by examining the enduring health consequences of childhood exposure to dynamic family structures, a common life experience for today's children. Findings will further our understanding of the ways in which the social environment gets under the skin to influence physiological functioning and biological processes that have consequences for health. Knowledge gained from this project will help more effectively target child welfare policies to crucial developmental periods, and to better understand and reduce health disparities. An interdisciplinary team of dedicated and highly skilled mentors developed a personalized training plan to support the Investigator in pursuit of her research and career goals. To accomplish the proposed research, the Investigator requires additional substantive and technical training in biology to be achieved through coursework, guided reading, seminars and workshops. The Investigator's professional development will be supported by strengthening her publication record, as well as her grant writing and communication skills. These activities will provide the Investigator with the training necessary to develop expertise in biosocial research and engage in productive interdisciplinary research at the intersection of social and biomedical sciences. The training will also facilitate the Investigator's transition to independent research, and enable her to attain her career goal of securing a faculty position at a leading research university.